Matrix Metalloproteinases (MMPs), a family of proteolytic enzymes that participate in cell migration and matrix degradation in order to maintain and remodel the tissue structure, are zinc dependent endopeptidases. They comprise a large family of proteases that share common structural and functional elements. These enzymes are primarily distinguished from other classes of proteinases by their dependence on metal ions and neutral pH for activity. Zymogen forms of MMPs (pro-MMPs) are secreted into the matrix of a large number of cell types. (Corbel 2002) Activation of the of the pro-MMPs in the local microenvironment can subsequently result in discrete alterations in the tissue structure. The MMPs can be classified into distinct subclasses, two of which are the gelatinases (MMP-2 and MMP-9) and matrilysin (MMP-7).
There has been significant interest in MMP inhibition as a therapeutic strategy. Metal metalloproteinase inhibitors (MMPIs) have been examined as therapeutic targets for various disease states. Animal models indicate that MMPIs could be useful treatments in inflammatory diseases such as multiple sclerosis, glomerulonephritis, bacterial meningitis, uveroentinitis, graft-versus-host disease, emphysema, aortic aneurysm and restenosis after angioplasty as a treatment for atherosclerosis. (Brinckerhoff 2002) Excessive levels of MMPs are also present in various respiratory diseases. Two MMPs, MMP-2 and MMP-9 have been implicated in development of airway inflammation and pulmonary fibrosis and the modulation of MMP activity by eliminating excessive proteolytic damage has been suggested. (Corbel 2001)
Tumor necrosis factor-α, TNF-α initiates most of the essential steps of inflammation, including the increased expression of other cytokines, chemokines and proteases like MMPs. It has been demonstrated that MMP-2, MMP-9 play a role in the mouse model of TNF-induced lethal heptatitis. (See Wielockx, 2004). MMP-7 deficient mice are much less vulnerable to TNF than wild type mice, indicating MMP-7 is also important during an acute and systemic inflammation induced by TNF administration. Id. MMP 7 inhibitors have been suggested for treatment of such diseases as cancer, inflammatory lung disease, Alzheimer's disease and atherosclerosis. Id.
To date however, only one MMPI, Periostat (doxycycline hydrate) is licensed in the United States. Periostat is used to treat perodontitis. Doxycline both inhibits MMP activity and also seems to decrease MMP gene expression.
As such, there is a need for more and better agents used to treat inflammatory diseases.
Also, there is a need MMPIs capable of inhibiting or modulating MMP activity, including the activity of MMP-2, MMP-9 and MMP-7.
MMP-9 is also implicated in diseases of the eye. MMP-9 is one of the primary matrix-degrading enzymes on the corneal surface, and an increased density and activity of MMP-9 was observed in the tear fluid of dry eye patients (Afonso et al., 1999; Solomon et al., 2001). In addition to its actions on matrix proteins, MMP-9 proteolytically activates latent precursors of IL-18 and TGF-β (Schonbeck et al., 1998) and increased expression of MMP-9, IL-1b, and TNF-α have been all found in mouse corneal epithelial cells following an experimentally induced model of mouse dry eye (Solomon et al., 2001; Chen et al., 2008b). MMP-9 has also been shown to be responsible for the destruction of corneal barrier in experimental dry eye mice (Pflugfelder et al., 2005). Compared with MMP-9 deficient mice, the wild type animal suffered greater corneal epithelial permeability and desquamation of differentiated apical corneal epithelial cells (Fini et al., 1996).
The ocular surface is covered by a tear film which is composed of three layers: the outer oil layer, the middle aqueous layer, and the innermost membrane/mucin layer associated with the apical corneal epithelium. An insufficient tear supply can cause a prolonged alteration or imbalance of the tear film components on the surface. Such conditions alter the homeostasis on the ocular surface by triggering stress pathways in the epithelial cells, which can lead to “dry eye syndrome (DES).” DES causes ocular damage which is very painful and debilitating and can lead to blindness in severe cases. It affects tens of millions of people worldwide. It is accompanied by increased osmolarity of the tear film and inflammation of the ocular surface.
In DES, the stress response made by the ocular surface epithelial cells initiates an inflammatory response by activating stress signal pathways in the epithelial cells to produce various inflammatory cytokines, chemokines, and components associated with the inflammatory process (Luo et al., 2005). The combined net result of such events is the recruitment of inflammatory and immune cells to the ocular surface. The recruitment of these cells induces a feed-back loop wherein the cell secretions induce corneal epithelial cell dysfunction and damage, which in turn leads to greater inflammation and leads to disease progression (Pflugfelder et al., 2008). Dry eye patients have increased levels of various inflammatory mediators in their tear fluid such as interleukin IL-6, IL-8, and TNF-alpha, and IL-12.
To date, however, treatments for dry eye disease have been inadequate. Clusterin (CLU), also known as apolipoprotein J, testosterone-repressed prostate message-2, or sulphate glycoprotein-2, is a secreted disulfide-linked heterodimeric glycoprotein (70-80 KD) that plays a role in multiple biological events including apoptosis, oxidative stress, sperm maturation, complement regulation, and cytoprotection (Shannan et al., 2006). Initially, CLU was thought to be a marker of cell death because its levels of expression increase in various lesions undergoing cell death. Recent studies have suggested that it also has a role in protecting cells from cell death, and has now become a target for certain cancer therapies (Chung et al., 2004). Following infection, the CLU levels increase as both a positive acute and chronic phase response protein in patients (Chen et al., 2008a) and animal models (Sharma et al., 2008).